Tissue Rolls: Tissue rolls are just the perfect size for hamster! They're small enough for them to neatly fit inside, yet long enough for them to drag some soft tissue into and turn it into a nice little home. Make sure to remove all of the 'glue' that some tissue companies use.
Paper Towel Rolls: These are a little longer, but usually about the same width as tissue rolls. They are great for making 'underground' tunnels that lead under bedding. Because of their length hamsters really love wandering through these.
Gift Wrap Rolls: These long tubes are great for cutting up and reconnecting to make twists and turns in tunnels. To make a turn, simply cut the edge at an angle, and connect it to another piece- also cut at the same angle. They will fit together nicely and make a perfect corner. Different angles make different corners, so get creative with it!
Old Sweater Sleeves: Cloth sweater sleeves make very unique tunnels. They can be hung up, folded into corners, and opened by simply placing a round bracelet on the ends. These are very comfy, but should be used with caution. Try to use natural fabrics like cotton, fur, and hemp- in case the fabric is eaten.